People who are planning for retirement are often going to pinpoint the date at which they become eligible to receive Social Security as their retirement date. It should be noted that it is not a good idea to be overly reliant on Social Security because the monthly benefit is rather modest and there are no guarantees about the future of the Social Security program.
An intelligently conceived retirement plan throughout your working career that reduces your dependence on Social Security will certainly help. And of course many people do not want to lose their employer-provided healthcare insurance by retiring before they became eligible to enroll in the Medicare program.
Currently everyone who has paid into the program sufficiently becomes eligible for Medicare at the age of 65, but Social Security is different. The age at which you become eligible to receive your full benefit will depend on the year you were born. Full retirement age is 66 for people who were born between 1943 and 1954. Full retirement age then rises by two months per year up to 1960. People who were born in 1960 become eligible to receive their full retirement benefit at the age of 67 as do those who were born after that year.
If you wanted to maximize your potential Social Security payout you could delay your application and continue working until you reach the age of 70. When you do this you gain delayed retirement credits that provide an increase in your monthly benefit by 8% for every year that you delayed applying for Social Security.
Conversely, you can also retire early if you want to. It is possible to begin receiving Social Security at the age of 62, but you would be receiving a significantly reduced benefit.
The above information is accurate as of this writing. It is however useful to recognize the fact that changes are always possible, and raising the eligibility age has been discussed as a way to save money on the program.